Implantable medical devices (IMD) can include, among other things, cardiac rhythm management (CRM) devices such as pacemakers, cardioverters, defibrillators, cardiac resynchronization therapy (CRT) devices, or neuro-stimulation systems such as spinal cord stimulation (SCS) systems, or combination devices that can provide more than one of these or other therapy modalities to a subject. An IMD can include or use an Integrated Circuit (IC) that can provide one or multiple power supplies such as to treat one or more living organs, for example, by pacing the heart. Since the IC generally controls the operation of the IMD, it can be important to protect the IC from damage caused by excess voltage supplied to the IC.
Excess voltage resulting in damage to the IC can be caused by electrostatic discharge (ESD). Electrostatic discharge (ESD) is the sudden and momentary electric current that flows between the plates of a capacitor at different electrical potentials. ESD can lead to momentary unwanted currents that may cause damage to electronic equipment. An ESD event can be characterized by its amplitude and spectral content, and can include a characteristic ESD event threshold. The ESD event threshold can be characterized as a characteristic voltage applied using one of the following ESD models: human body model (HBM), machine model (MM), or charged device model (CDM).
In order to avoid the electrostatic discharge, an ESD clamp can be used. The ESD clamp is a circuit that can be configured to divert a potentially damaging charge away from the sensitive circuitry and protect the system from damage. An IC with multiple power supplies can use one or more protection circuits, such as between adjacent bond pads, to inhibit or prevent the damage caused to the IC by an excess voltage supplied to the IC. The ESD clamps can have a high-pass filter characteristic so that they respond to ESD events (which have high spectral content, or rapid change in voltage) without responding to non-ESD voltage excursions, such as can occur during or after the device is powered up. ESD clamps can have high pass filter characteristic time constant (T), e.g., ranging from 0.1 microsecond to 1 microsecond.